The present invention relates to a grooved refractory component, and more particularly to a pouring tube, for pouring a molten metal between an upper metallurgical vessel and a lower metallurgical vessel, a refractory assembly incorporating such a component, and a casting installation incorporating such an assembly.
It is known that the continuous casting of steel calls for the filling of successive metallurgical vessels, notably a ladle, a tundish and ingot moulds, and that during its passage from an upper metallurgical vessel to a lower metallurgical vessel, the metal must as far as possible be kept out of all contact with the ambient air.
To this end, a pouring shroud or a submerged entry nozzle made of refractory material forms an extension to the pouring orifice of the upper vessel (respectively the ladle or tundish), and enters the bath of molten metal present in the lower vessel (respectively the tundish or ingot mould), so that the molten metal passes from the ladle to the tundish or from the tundish to the ingot mould without ever being exposed to the ambient air.
The pouring orifice of the upper vessel incorporates an inner nozzle in refractory material, which opens below this vessel via a contact surface designed to mate with a contact surface on the pouring shroud or submerged entry nozzle, thereby forming a joint face between these two components.
Conventionally, a casting installation also includes means of regulating the flow of the molten metal. These means may consist of a stopper rod which enters the metal bath of the upper vessel opposite the pouring orifice and whose degree of immersion in the said metal bath determines the opening of the said pouring orifice. Alternatively, use may also be made of a slide valve incorporating a set of refractory plates each having an orifice. These plates are normally located between the inner nozzle and the pouring shroud or the submerged entry nozzle. The degree of alignment of the orifices in adjacent plates determines the flow of molten metal.
A continuous casting installation therefore includes numerous assembled refractory components, the interfaces between which are formed by contact surfaces that may be planar or non-planar, as indicated for example in document U.S. Pat. No. 5,984,153.
It is known that the reductions in cross-section which occur along the molten metal pouring channel produce considerable negative pressure which can in turn lead to an induction of air. To avoid the penetration of air through the joint surface between two adjacent refractory components, conventional practice involves injecting an inert fluid, more particularly an inert gas such as argon, into an injection groove formed in the contract surface of one of the components and which delineates, in conjunction with the contact surface of the other component, a gas injection channel which nearly completely encircles the molten metal pouring orifice.
The risks of the metal coming into contact with the ambient air are thus effectively reduced during its passage from the upper vessel to the lower vessel.
More recently, documents WO 98/17420 and WO 98/1741 have also shown that the injection channel can effectively perform the additional function of allowing the injection of a sealing agent, such as graphite for example, to fill cracks propagating from the pouring orifice in the contact surface of one of the components, or score marks or scratches oriented in the general direction of movement of one of the components during its replacement. The sealing agent, which is conveyed by a carrier fluid, limits damage to the refractory around the cracks and/or score marks or scratches, thereby preventing the induction of air through these. The injection channel may be open or closed. In the description which follows, the terms injection channel or injection groove will be used equally to describe a channel or groove intended for the injection of an inert gas alone or a sealing agent in a carrier fluid.
The injection channel is therefore very useful. The applicant has found, however, that in certain cases this channel may itself become clogged, i.e. blocked.
In particular, this phenomenon has been observed in the case where the injection groove is formed in a surface of a refractory pouring tube bearing against the surface of another refractory component (a pouring tube) intended to be replaced during casting operations. For example, when the injection groove is formed in the lower surface of the inner nozzle bearing against the upper surface of a pouring shroud or a submerged entry nozzle.
Although the invention is clearly not limited to this particular case, for reasons of convenience it will be described in the description which follows with reference to an injection groove formed in the lower face of an inner nozzle bearing against the upper face of a submerged entry nozzle.
Replacement of the submerged entry nozzle can be carried out, in a known manner, by positioning a new submerged entry nozzle beside the submerged entry nozzle to be replaced, then simultaneously moving the two nozzles, allowing the new nozzle to displace the worn one and take its place beneath the inner nozzle.
Prior to each replacement, the tundish pouring orifice is closed off, but it is possible for a certain quantity of molten metal to remain at the joint surface, at the interface between the pouring orifices of the inner nozzle and the submerged entry nozzle. This metal is drawn into the joint surface as the nozzle is moved, and accumulates in the inert gas injection groove thereby blocking it, which renders it ineffective both in terms of the admission of ambient air and in terms of the treatment of cracks and score marks or scratches by means of a sealing agent conveyed by the carrier fluid.
The aim of the present invention is to remedy this shortcoming in a simple and economic manner.
The object of the present invention is therefore a refractory pouring tube forming part of a pouring channel and including at least a first contact face capable of bearing against a second contact face of another refractory component forming an adjacent portion of the pouring channel and provided with an injection groove forming, in conjunction with the first contact face, a fluid injection channel at least partially encircling the said pouring channel, the said pouring tube being arranged to be displaced in a predefined trajectory along which the first contact face slides and remains in bearing contact against the second contact face, whilst the portion of the pouring channel formed by the said pouring tube intercepts a determinate part of the injection groove, characterised in that the first contact face incorporates an additional groove positioned so that, in the pouring position, it is located in proximity to the determinate part of the groove and communicates with this groove at least on either side of this determinate part.
The refractory pouring tube is for example a submerged entry nozzle or a pouring shroud. The additional groove formed in the contact face allows the injected fluid to bypass the obstructed part of the injection groove.
In this way, even if the injection groove is obstructed, the injected fluid is able to circulate completely around the pouring orifice and form a barrier to the ambient air.
An advantageous characteristic of the invention is that the additional groove is formed in the refractory pouring tube which is regularly replaced, so that the injection channel is cleared each time this pouring tube is replaced, unlike the situation prevailing in the current state of the art where replacement of the refractory pouring tube causes the injection channel to become obstructed.
It is to be noted that the additional groove cannot be too large; for example, it cannot completely encircle the pouring orifice (such as in the tube disclosed in document WO 92/20480), otherwise, the additional groove could not serve as a bypass for the injected fluid where a part of the injection groove is obstructed. On the contrary, a groove encircling completely the pouring orifice would form a shortcut for the injected fluid, preventing thus the metal from being efficiently protected by the injected fluid. Preferably, the additional channel is blind so that the pressure in the injection channel is maintained.
According to a particular characteristic, the additional groove is formed to cover the outlet of a delivery and/or discharge conduit (if any) of the fluid injection channel. This outlet is thus better able to clear itself in case of obstruction.
Preferably, the additional groove should have a width such that, when the groove is at the level of the pouring orifice (for example when the tube is changed), it does not communicate with the injection groove. Thus, if some molten metal remains at the interface between the pouring orifices of the inner nozzle and the submerged entry nozzle, it will not reach the injection groove. Therefore, according to an advantageous characteristic of the invention, the additional groove is shorter than the minimum width between opposite sections of the injection groove on either side of the pouring orifice at the level of the pouring orifice.
According to another particular characteristic, the first contact face incorporates a second groove essentially parallel to the additional groove. This second groove may be located, relative to the additional groove, on the other side of the pouring channel. The function of this second groove, referred to below as the scraper groove, is to scrape the contact face incorporating the injection groove to clean it of any dirt or extraneous material liable to impair the contact quality between the two faces, before the new refractory pouring tube is placed in position.
Advantageously, the scraper groove is symmetrical with the additional groove relative to the pouring channel. The two grooves are therefore interchangeable, which makes it possible to insert the replacement pouring tube without needing to take into account its direction of movement. According to its position relative to the injection groove, each groove performs the function of additional groove or scraper groove.
The object of the present invention is also an assembly of refractory components forming a pouring channel, a first component of the assembly incorporating at least a first contact face bearing against a second contact face of an adjacent refractory component, with a groove being provided in the second contact face to form, in conjunction with the first contact face, a fluid injection channel at least partially encircling the said pouring channel, characterised in that the first component is a refractory pouring tube such as that described above.
According to a particular characteristic of this assembly, one or certain of the refractory components incorporate a delivery conduit and, where appropriate, a discharge conduit for the fluid injection channel.
The object of the present invention is also a casting installation including an upper metallurgical vessel and a lower metallurgical vessel, connected by a pouring channel defined notably by an assembly of refractory components as described above, the installation also including a fluid source connected to the delivery line of the fluid injection channel.
In a particular embodiment, the casting installation also includes a means of injecting a sealing agent into the fluid.